People with HIV/AIDS survive to older ages, but we still do not know if or how HIV-associated neurocognitive disorders (HAND) is exacerbated in the aging brain. We will evaluate the hypotheses that brain inflammation drives an interaction between HAND and brain aging by modifying the ubiquitin proteasome system (UPS). The UPS is the main route of neuronal protein turnover; it is required for normal minute-to-minute physiological changes in synaptic potentiation, learning and memory formation. The UPS plays a key role in preventing the accumulation of misfolded neuronal proteins in pathological neurodegeneration during brain aging. We established that the UPS is abnormal in brain cortex of people with HAND: Immunoproteasomes (IPS) are induced in response to interferons. IPS induction was linked solidly with HIV-associated neurocognitive disorders (HAND). It was relevant pathologically because it was prevalent in subjects with HIV encephalitis (HIVE) and/or replicating HIV concentration in the brain. It was anatomically pervasive in critical neuronal compartments including synapses, axons and neuronal nuclei, perikarya, and isolated synaptosomes. The proposal will test the hypothesis that IPS induction perturbs the synaptic protein economy by diverting the UPS substrate repertoire pathologically, which alters the substrate repertoire, synaptic protein turnover, and synaptic plasticity in HAND and brain aging. The first aim will use human brain specimens to determine how IPS induction affects macromolecular assembly and enzymatic functions of the UPS, including the dynamic interaction with synaptic proteins. The second aim will use interferon-stimulated mixed brain cell cultures to determine how IPS induction influences synaptic protein turnover and holoenzyme kinetics, and will determine whether inhibiting the IPS reverses these changes in the synaptic protein economy. A final aim will use autopsy specimens to determine if the age-of-onset or rate-of-accumulation of misfolded proteins during pathological brain aging is perturbed in association with IPS induction. The program overall addresses a highly novel mechanism for synaptic dysfunction in HAND and has important implications for the mechanism of interaction between pathological brain aging and HIV/AIDS.